Curable compositions are often used to encapsulate electronic components. These encapsulating materials must be self-extinguishing in the case of ignition. Commercially available compositions for encapsulation typically employ a combination of halogenated aromatic compounds and antimony oxides to achieve flame retardance. However, the halogenated aromatic compounds interfere with the recycling of electronic devices, and concerns have been raised about health effects associated with antimony oxides. There is therefore a need for flame-retardant encapsulant compositions that reduce or eliminate halogenated aromatic compounds and antimony oxides while maintaining or improving the balance of toughness, heat resistance, and moisture resistance.